&#;Magic mirror, on the wall &#; who is the fairest one of all?&#;.
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While this guide won&#;t provide answer to the Queen&#;s request in Disney Classic, Snow White and the seven Dwarfs, you&#;ll get a glimpse of the optical mirrors offer you can find on the market and select the best mirror that may fit your needs.
An optical mirror is a precision optics component made of a optical polished substrate material and a high reflection coating. It can be of various shape and dimensions from less than a millimetre to several meters.
Optical mirrors are found in all the Photonics applications : in astronomy inside every telescope, in lasers by design, in vision equipment, and most of the optical assemblies systems. While their usage is quite simple : reflect the light, their range of application is wide, from UV to IR it can be used to transmit light with a change of direction, to focus light (for example in a Cassegrain telescope) or pumping light in a laser.
Under the name &#;mirror&#; are many different types of precision optics that may be sorted as one of below type :
Mirrors substrate material are usually selected for their good shape resistance to temperatures changes, easiness of coating to bound with it and easiness of polishing to guaranty a good polishing shape. For some high power laser applications, substrate can also be the in LIDT constraint and therefore be selected carefully.
Below table shows most common substrate material for mirror blanks :
Substrate material Remarks Float Very cheap material that comes with acceptable polishing and flatness level for low requirement applications. Fused silica Resistant material with good optical machining properties, very commonly used. N-BK7 / H-K9L Most common optical glass, can be used for high requirement surface aspects. Zerodur Material almost non affected by low temperature, used mainly for space applications. Metals Polished aluminium or brass can be used for some high power laser applications, they are also easier to machined than glass type material and mechanicaly stronger. Plastics Plastic substrates are used in optical applications, but the difficulty to keep a good surface quality and the easy wearing of the parts due to outside environment limit its usage, while this remain the cheapest substrate material.Remark : for some applications where mirrors maybe of important dimensions and the part weight is an important constraint like in space industry for example, a lightening of the part can be done with a structuring of the back of the substrate.
The most important part of an optical mirror is its high reflection coating, it is that coating that will be at the interface of incident beam and reflect it to an orthogonal direction.
With the improvement of vacuum deposition equipment in the last 30 years, layer of dielectric material can be deposit of substrates with a nanometric precision.
The material and the thickness used for each layer enable the trimming of a broadband of wavelengths where the incident beam will be reflected.
It has to be noted that the reflection of such mirror degrades as the AOI increases.
*Metal coatings are protected with SiO2 layers in order to avoid corrosion.
**An additional Chromium layer is usually added between the substrate and the metal to improve adhesion.
The critical specification for optical mirrors to be used in laser applications is their LIDT (Laser Induced Damage Threshold, or in short Damage Threshold).
This specification often measure in J/cm2 defines the energy that can be accepted by a surface area. (for reminder Watts are defining a power so values in Watts should be integrated in the time to be translated to energy).
LIDT should be defined with detail of the type of reference laser : CW or pulse laser, pulse duration, frequency and power.
Usually the coating is the contraint before the substrate, but for high power laser substrate can be wear by laser usage too. The lower the polishing and the higher of impurities in the material will bring to lower LIDT of the substrates.
Deformable mirrors are active optics elements used in adaptative optics. They are typically made of an optical membrane, actuators and an electronic controller.
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Their main usage is compensating aberrations, from example of the atmosphère in astronomy, of the eye in ophthalmology or of the cells water in biomicroscopy.
Main suppliers of deformable mirrors are ALPAO and ISP-System for high power applications.
What are Hot mirrors and cold mirrors ? It is rather intuitive (while sometimes confusing) :
In a nutshell : Hot mirrors reflect warmth, cold mirrors reflect cold signal.
They are used to separate visible to IR parts of an optical signal.
Like most optical components optical mirrors are bought from precision optics manufacturers & distributors. It is rather common that the substrate and the coating are made in two different site, therefore buying mirror blank and doing the coating in-house or subcontracting it to other supplier is common practice.
Don&#;t hesitate to contact SINOPTIX for your questions about optical mirrors or to request for a quote.
Optical mirrors are precision optics with a highly polished plane or curved surface which reflects light. At Shanghai Optics we manufacture custom optical mirrors for a wide range of applications. Life Sciences, astronomy, metrology, and solar engineering are only a few of the industries which depend on our precision mirrors and other optical components.
Our state of the art machinery allows us to manufacture high quality mirrors designed to reflect a certain wavelength range while allowing light transmission in other wavelengths. Custom optical mirrors and precision reflectors can also be designed to reflect at pre-specified angles.
Our broadband dielectric mirrors are ideal for demanding applications. Durable and stable, they offer near total reflection over wide spectral ranges (up to 100s of nanometers) and can be used over wide angles of incidence. These mirrors are resistant to environmental or laser damage and are suitable for visible, NIR, and UV light.
Broadband metallic mirrors also offer high reflection over a broad spectral range. They are easy to set up, being insensitive to angle of incidence and polarization. We often recommend these coated mirrors as a good combination of performance and value.
We also manufacture high performance ultra-broadband metallic mirrors. Here the substrate is coated first with a reflective metal film and then with a dielectric overcoat. Our metallic coatings include aluminum, silver, or gold. Gold is ideal when working in infrared applications, especially at wavelengths greater than 2 micron. Silver has high reflectance over the visible and near infrared range. For a general purpose visible range, an aluminum coating performs well. The final dielectric coating provides protection and enhances reflectivity, and these mirrors are highly durable.
For applications with a specific, narrow wavelength and higher energy levels, we recommend laser line mirrors. These highly efficient precision mirrors can be used for beam-steering in laser applications. Our laser line mirrors can be customized for your specific laser beam type or wavelength, and we offer dielectric coatings that can be optimized for high reflectivity at your laser wavelength of choice.
Other Specialty Optical Mirrors
Our parabolic mirrors are designed to reflect energy from a single point outwards, or to capture all parallel incoming rays and reflect to a single focal point. They have many applications including laser material processing, fluorescence microscopy, high harmonic generation, and super continuum generation without wave guides.
An off-axis parabolic mirror can be considered to be a &#;cut out&#; from a larger parent parabolic mirror. These mirrors are a bit more difficult to align, but when properly set up can be extremely helpful in optical design. They exhibit many of the same features as parabolic mirrors, but will deviate light off-axis. This allows for more interactive space around the focal point.
Spherical mirrors with concave surfaces may be used to form either real or virtual images, depending on the placement of the light source. These mirrors curve inward. They are ideal for focusing light to a single point.
Convex spherical mirrors bulge out toward the light source, with a curve that resembles the exterior of a sphere. Images formed with these mirrors will always be virtual, reduced in side and right side up.
Right angle mirrors are made from right angle prisms, with a special metallic coating on the hypotenuse of the prism. These mirrors are ideal for system alignment, being easily mounted. They reflect light back at a 90 degree angle. Right angle mirrors are also known as turning mirrors.
If you are looking for more details, kindly visit Custom Optical Mirrors.